1. Field of the Invention
The present invention is related to a fabrication method for fabricating a compound semiconductor device and a method of fabricating the same, and is especially related to the most effective technology to be applied to fabricate a Schottky diode, a MESFET (Metal-semiconductor Field Effect Transistor), etc. on a InP single crystal or its ternary or quaternary mixed crystal substrate.
2. Disclosure of the Prior Art
Even though much research has been performed on compound semiconductors such as GaAs and InP, having electron mobilities higher than that of Si and being radiation resistive and heat resistive, which semiconductors are considered to be promising for the future high-frequency and high-speed electronic devices, MOSFETs formed of such compound semiconductors have not yet been put to practical use because stable oxide layers with low interface level density can not be obtained. In the case of GaAs, MESFETs are put to practical use and thereby discrete high-frequency FETs and small scaled digital ICs are put to practical use. GaAs MESFETs have, however, a disadvantage in that it is impossible to fabricate large scaled digital ICs with the high fabrication yield because the Schottky barrier voltage is small and the logic amplitude is not large.
On the other hand, since InP has a large electron saturation velocity, the thermal conductivity being 1.5 times larger than that of GaAs and the break-down voltage being large, the application of InP for FETs is investigated with the expectation that it may be a material for super high-speed devices, especially high output super high-frequency devices.
InP has however a disadvantage that the reverse leak current is too large and the gate voltage is too small for its practical use because the Schottky barrier height of InP is small (0.3-0.4 eV) compared with GaAs (0.8 eV). In the case of InP, many investigations have been therefore performed on MISFETs by depositing insulating layers such as SiO.sub.2, SiN.sub.x, Al.sub.2 O.sub.3, PN.sub.x at low temperatures by CVD, plasma CVD, light-excited CVD, sputtering and evaporation methods.
MISFETs with good properties however could not be obtained because interface level densities between the insulating layer and the substrate are considerably large even for MISFETs with insulating layers grown by low temperature deposition.
There is also a technology related to diodes and MESFETs with improved Schottky barrier height wherein cadmium metal is deposited with the thickness of 200 A on an InP substrate or on an InGaAs substrate and a Schottky electrode is formed on Cd metal (Appl. Phys. Lett. 58(1991), 25).
This technology can considerably improve the Schottky barrier height but it is still limited to 0.55-0.70 eV.
The present invention has been developed under the above mentioned circumstances. It is an object of the present invention to provide MESFETs and Schottky diodes on III-V compound semiconductor substrates, having Schottky electrodes with good characteristics such as a low reverse current and a high gate breakdown voltage, and a method of fabricating the same.
It is another object of the present invention to provide InP MESFETs and InP Schottky diodes which have a Schottky barrier height comparable to that of GaAs, and a method of fabricating the same.